Monitoring 12dvc motor speed

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Mike77z

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Hi Guys,

I stumbled on you forum off a google search and i was wondering if any of you gentleman/ladies would be able to answer this question for me.

I have a 12v dc electric motor ( 9.2A startup 6.7A constant )that runs a water pump. I would like to be able to monitor the motor to make sure the impeller is spinning. It could be as simple as a LED that turns on when its not seeing the motor run.

I found a circuit that appears to do something like i want but with a speed controller ( which i have no use for ) HERE. Its been a while since i was last working with circuitry and im hoping you folks may have a better idea of what i should look into doing

Regards Mike
 
I'm supprised with all the knowledge i seeo n this site that nobody has any ideas , Is it possible that im asking the impossible to do what i want ?
 
Why not just put an indicator light on the motor 12v line. When power to the motor is applied, the light comes on telling you the motor is on.
 
That was an option aswell but if the pump stops turning and does not blow the fuse the indicator will still say the motor is running. Its in a race car application its one of those things if the pump stops working it could be very costly.

Having the ability to say the motor is functioning would just add to piece of mind after having a 12 thousand dollar mistake happen to a friend of mine i don't want to take the risk if i don't have too, but i may just have to do exactly that

Thanks Mike
 
Do you have a picture of this motor and it's installation?

Without sticking a sensor on the motor itself or tapping into the line the impeller is in, I would say a current sensor measuring the motor current might work since if you stop a motor that is being powered the current will spike up and burn out the motor. However, it seems to me that you might notice this (or maybe not). WIthout knowing why the impeller might stop turning I can't say much more.
 
Last edited:
Mike77z said:
I have a 12v dc electric motor that runs a water pump. I would like to be able to monitor the motor to make sure the impeller is spinning. It could be as simple as a LED that turns on when its not seeing the motor run.
Click to expand...

I see three ways to monitor whether Mr. motor is actually spinning: 1) monitor the motor back-EMF, as the referenced article shows, 2) have the motor also drive a tach, or equiv, to generate a signal of your choosing, or 3) place a pressure or flow sensor in the fluid being pumped.
 
Is the impeller hard coupled to the motor or magnetically coupled?

John
 
**broken link removed**

Is the pump I'm using, i have been waiting on it to arrive from the supplier ill post a actual picture of it when it arrives if you guys want.

Its mostly the in case factor if a foreign body got in the cooling system ( IE spring from the lower rad hose breaks and lodges in the impeller as happened to said friend of mine )

AS far as the Back- EMF curicuit im assuming after looking at the circuit again that would be the simplest of methods ?
 
It looks like an electric water pump for a Chevrolet. Couldn't you use the water temp gauge to verify that it's cooling? Or is the pump on another device?
 
Its a water pump for a big block chevy the problem is the kinda of heat it builds if the waterpump fails by the time i notice it on the gauge it will more then liekly have already wrecked the crank bearings. I'm just one of those people that if i can with a reasonable ammount of effort make something that will A give me piece of mind and B Ok ill admit it add a wee bit of a cool i made this factor i would love to do it

The unfortunate thing that i hav e noticed after talking with a few friends including my engine builder is if the motor on the pump fails and i say notice it via the engine temp say hitting 220 f by the time i get it shut down the motor will more then likely have peaked over 260 f.

The monitor circuit that we have talked about that the back emf monitoring seems like the way to go but unfortunately my electronic knowledge does not allow me to look at the diagram and remove the speed controler. Speaking of which can it be romved from the build and still function as a monitor easily ?


Thanks guys its truthfully appreciated , i will post some pics of what im doing this for tomorrow


Mike
 
If you monitor motor current you would get instant feedback of a motor failure on a gauge, like no current, max current etc. I suppose while your speeding down the track, you may not look at a gauge.
 
Yup current sensing is probably the easiest. I wasn't sure if you were more worried about the motor stopping spinning or something like the impeller breaking where the motor keeps on spinning but the impeller doesn't.
 
dknguyen said:
Yup current sensing is probably the easiest. I wasn't sure if you were more worried about the motor stopping spinning or something like the impeller breaking where the motor keeps on spinning but the impeller doesn't.
Click to expand...

See now there is another one that was also thought about. But im asking enough , i saw a flow meter from someone on the internet i may take a look at but it will need to output to a warning light.

<b>Mikebits If you monitor motor current you would get instant feedback of a motor failure on a gauge, like no current, max current etc. I suppose while your speeding down the track, you may not look at a gauge. </b>

Thats the issue with the gauge but its true that hte current monitoring is prolly the simlest since even if the impeller came off the motor the load/current would drop since it was just free spinning in liquid but also hard to look at another gauge.

Also the new dash i just ordered this morning
**broken link removed**

Thanks Mike
 
hi mike,

I have circuit, which detects the extra current that flows in the 12v line, when the motor is not rotating.

Its logic is like, 0.05 ohms resistor is kept in series with the 12v line and during the normal running conditions the drop accross the resistor would be 0.326v.

Whenever the motor is still, the current would increase, thereby increasing the voltage drop accross the resistor. The increase in drop can be identified by a comparator. The comparator output drives the LED.

Whenever the motor is still the LED glows. I have attached the circuit schematic.


Note: The circuit is not tested. This is just a rough design.
 

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Thanks Beenuseren, Ill try building that this week and let ya know how it works out once the pump arrives should be just as easy as removing the motor and stopping the impeller with my hand i would guess * or just using another motor

Regards Mike
 
Two pressure sensors; at inlet and outlet being read by a differential amplifier will tell if it is pumping.
A single differential pressure switch can also be used to turn on a lamp/buzzer.

Miguel
 
Now in a engine application would that work where there is a residual say 16 psi in the cooling system ? I suppose you are just comparing the pressure to see if there is more pressure on the pressure side then the intake side i suppose


Regards Mike
 
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